Out on the edge of Arizona's Painted Desert, about 100 miles outside Flagstaff, sits an extinct, brown, volcano cap. Over the last 30 years, the cone's rim has been coaxed into an elliptical form, whole flanks of its sides have been degraded and rebuilt, wide tunnels have been dug, an amphitheater is planned, and 23 viewing rooms will eventually be tucked and hidden into its sides.

Construction is both so delicate and so substantial that a company specializing in such huge civic structure as dams and baseball stadiums has been contracted. Some of the volcano's resulting subterranean rooms will be best used during solstice or equinox; others will focus starlight onto the walls in the manner of a camera obscura; one, perhaps, will allow visitors to stand in the very shadow of the planet Venus.

Once completed (gamblers take bets on 2005), all of this work and expense--topping $15 million--will result in a huge earthly bump that, from the outside, looks just like an extinct, brown, volcano cap. But from the inside, humankind's palpable experience of the firmament itself will have been redesigned. This natural relic of unnatural alteration called the Roden Crater will have been reshaped and reformed by the influence of one man into a 21st-century monument with a resulting power and intention akin to Stonehenge.

That man is James Turrell, an artist whose pursuit of light has caused him to attempt the most audacious of mortal acts: the deliberate reshaping of the earth's face so that humans may perceive the sky's ether differently. Perhaps even more audacious, given all of the tractors and earthmovers involved, is that Turrell's artwork isn't about light; it is light.

Quickly becoming an oversized American legend due to a recent and lengthy New Yorker magazine profile and the New York Times' slavish reportage of his original patron the Dia Art Foundation, Turrell is a trained mathematician and psychologist brought up in the Quaker tradition who won a MacArthur Fellowship "genius" grant at the age of 41.

He now runs a cattle ranch to support the construction of the Roden Crater and shrugs that he has sacrificed two marriages and numerous relationships to this most primary love. A licensed pilot and antique airplane mechanic who, myth says, flew missions into Tibet during the early '60s in order to rescue monks from the Chinese invasion, James Turrell is also arguably the most important artist working in the West today.

Fritz Frauchiger, the former director of the ARCO Center for Visual Art who exhibited Turrell in the late '70s, says, "He's got the most interesting mind. He's thinking cosmically at all times, and the best way he had to understand perception was to investigate light and space."

Turrell's investigations edge closer to this side of the continent when he appears at the Sonoma County Museum's welcoming reception of his work, titled "James Turrell: Light and Land," this June 21.

In part coordinated with San Francisco's Exploratorium and supported by grants from the NEA and others, "Light and Land" features Turrell's work in two sections. The main gallery of the museum's 1908 Federalist building now houses a huge boxlike structure in which is displayed Sebastopol collector Carol Vena-Mondt's privately owned piece of early Turrell exploration, Raemar.

Last exhibited to the public in 1976, Raemar uses the manageable trickery of artificial light to challenge that most ordinary of our perceptions: sight. Utilizing 12 fluorescent bars, Raemar causes the eye to confuse one of the box's sheetrock walls instead as a floating element, bold blue, haloed, and ethereal.

(When Turrell showed a similar type of illuminated mirage in 1980 at New York's Whitney Museum of American Art, several weary visitors mistook the light for a wall, leaned upon its nothingness, and fell smack down upon the museum's floor. One such art victim actually sued Turrell for damages and temporarily won; the conviction was overturned on appeal. Writing about that exhibit in Time magazine, populist critic Robert Hughes praised the artist for having "contrived an exquisite poetry out of near emptiness." Hughes also knew well enough to stand up straight.)

In another room, live feeds from the Roden Crater are featured, as well as drawings, aquatints of various views to be had from within the crater, and models of two new aspects--the North and South spaces, yet to be built--of this maverick project. The South Space will, according to museum literature, act like a dish telescope, collecting not radio waves but starlight.

The North Space is planned to be a type of camera obscura reflecting the individual points of the Milky Way onto white sand below. Should they give the experience enough time, visitors to the North Space will be able to actually feel the earth's rotation as a visceral event.

Patience is an important factor in savoring and, indeed, actually experiencing Turrell's work. He sometimes creates black spaces in which only a sustained visit reveals the amount of light actually at play within the void. Entering one of his "skyspaces" (the Platonic ideal of a window, skyspaces shape outdoor light in a seemingly three-dimensional manner) or beholding one of his artificially lighted pieces may provoke irritated discomfort from the harried viewer. As when entering a dark room from outside, his work demands that you allow time for the eye to adjust.

Speaking to the Phoenix New Times in 1999 (Turrell didn't respond to repeated interview requests from the Bohemian), the artist said, "We weren't made for bright light because it almost completely closes our eyes. We're made for twilight. That's when our eyes truly open and feeling goes out of them like touch."

As with a marvelous riddle, Turrell's work leads inquiry down an unfamiliar path. If eyes can feel like touch, where can perception find itself bounded? What assumptions do we bring to sight, and what shorthand do we visually write that allows us to collectively decide that a green is a green or that a particular set of forms composes an apple? Hughes--who celebrated Turrell's work with such articulate brilliance in his American Visions book and TV series--concludes in the same Time review that Turrell's art "is not in front of your eyes. It is behind them."

Behind the eyes then, where our brains make minute and instantaneous connections, allowing us the sanity to pursue daily activities without ordinarily being struck dumb by the immense beauty of every single thing around us. It may be said that our brains work too well that way, and that being struck dumb by immense beauty is in itself a worthy daily activity. Turrell is among those adepts who can lift the dulled veil that the mind seeks to soothingly lay, refreshing our necessary perceptual intake with information that we simply didn't know to seek.

Seeking a further vision itself and in salute to Turrell's logging of hundreds of flight hours scanning the ground for the right spot before finding the Roden Crater in 1974, the SCM devotes the upstairs portion of "Light and Land" to aerial views of our patch of land, titled "Over Sonoma." Museum director Natasha Boas commissioned Los Angeles-based Center for Land Use Interpretation director Matthew Coolidge to shoot Sonoma County from the sky. "He's discovered things that people living here may not know even exist," she assures.

Another ancillary exhibit also culled from the Center for Land Use Interpretation, "Formations of Erasure" examines what has happened to various "earthwork" art projects over the years. Of particular note are photographs of Spiral Jetty, Robert Smithson's 1971 installation in Utah's Great Salt Lake.

Inevitably subsumed by the surrounding water, this stone curl extending from shore into lake rose again above the water line last autumn, ghostly and mossy and drippy. Smithson, who died in 1973, knew that the Spiral Jetty would sink when he created it; he may not have anticipated its rocky reappearance.

Frauchiger, who considers Turrell a friend, knows that unlike Spiral Jetty, the Roden Crater is intended to last. "It's his main direction, to get that thing done in his lifetime. But," he chuckles, "it's like the Winchester Mystery House--as long as he can tinker with it, he will."

Later, commenting on how enriched he feels having worked with the artist at ARCO, Frauchiger says firmly, "Some artists have no vision whatsoever; Jim is all vision."

'James Turrell: Light and Land' exhibits June 21-Jan. 4, 2004, in conjunction with 'Formations of Erasure' and 'Over Sonoma.' A public reception with Turrell is slated for Saturday, June 21, 4-6pm. He returns to speak at Sonoma State University on Sept. 16 as part of a series of supporting educational events. Sonoma County Museum, 425 Seventh St., Santa Rosa. Museum hours are Wednesday-Sunday, 11am-4pm. Admission is $2-$5; free to members. 707.579.1500.